docs: def to_file_path(self, path_prefix):
          """Write the embedding matrix and the vocab to <path_prefix>.npy and <path_prefix>.vocab.
  
          :param (str) path_prefix: path prefix of the saved files
          """
          with self._path_prefix_to_files(path_prefix, 'w') as (array_file, vocab_file):
              self.to_files(array_file, vocab_file)